1. Field of the Invention
The present invention relates to means for repeatably attaining the desired configuration of a cathode ray tube (CRT) front panel, or faceplate, of the tensioned mask type. Such CRTs may have the shadow mask mounting means affixed directly to the CRT panel. The CRT panel also carries the image forming screen of the CRT, which is, generally, a matrix of phosphor elements.
There have been proposed a variety of ways and means for making CRTs having interchangeable screens and shadow masks in order to simplify the manufacture thereof. However, any interchangeable system requires that the standard screen matrix be reproducibly positioned on each faceplate so as to register with any standard shadow mask. It will be remembered that the shadow mask apertures and the phosphor elements must register, i.e. be in operational alignment, for a suitable image to be formed on the screen. It follows that the substrates onto which the screen matrices are deposited, i.e. the screening surface of the CRT panels, must have a consistent configuration.
2. Discussion of the Related Art
As previously noted, tensioned mask CRTs may have the mask mounting means affixed to the faceplate. While this construction affords a multiplicity of advantages, certain problems concerning panel glass strain are attendant therewith. An improved system for affixing the mask mounting means is disclosed in the above-cited related U.S. patent application, Ser. No. 07/458,129, now U.S. Pat. No. 5,086,251, issue date, Feb. 2, 1992. Therein, the coefficients of thermal expansion (or contraction, if preferred, hereinafter CTE) of the mask mounting means, sometimes referred to as rails, and the panel glass are deliberately mismatched, with the mask mounting CTE being lower than the glass CTE to provide the panel assembly, i.e., the panel with its attached mask mounting means; with resistance to damage from thermal processing.
However, as is evident from FIG. 5 of that disclosure, included herein as FIG. 1, the panel assembly is distorted from its there desired flat shape by the disclosed system, resulting in a panel assembly distorted convexly toward the screening surface, as seen in FIG. 4.
Such distortion is not desirable where the registration and proper operation of an interchangeable mask and screen would be predicated upon the geometries of a planar panel assembly whose screening surface is flat to within, e.g., plus or minus one-quarter of a mil (0.00025 inches). It will be appreciated by the artisan that a cylindrical panel assembly utilizing a tensioned mask would have much the same requirements for repeatability of the desired geometry.
Therein lies a desiderata for such panel assemblies which are resistant to thermal shock and, as well, provide a repeatable configuration for the application of the phosphor screen.